1. Field of the Invention
This invention pertains generally to optical and magneto-optic head devices, systems and methods for reading magneto-optical media, and more particularly to a near-field hybrid magnetic-optical system and method wherein one or more small aperture semiconductor lasers and one or more magnetic read and/or write elements are formed on a slider as a single, integrated monolithic device.
2. Description of the Background Art
The optical head of an optical read/write system can operate as a xe2x80x9cflying headxe2x80x9d wherein the optical head does not contact the adjacent optical medium, but is positioned close to the optical medium and separated by an air gap. The optical head includes an aerodynamically designed slider with an air bearing surface for maintaining an air cushion between the optical head and the optical medium. One or more solid state lasers are typically mounted on the slider and are positioned to read and/or write onto the optical medium. The slider is typically mounted on a read arm by a spring mechanism, with the bias of the spring mechanism and the aerodynamic shape of the slider determining the distance between the optical head and optical medium.
Conventionally, the solid state laser and slider are separate components made of different materials. The slider, for example, may comprise a metallized SiC or TiC/Al2O3 body which has been appropriately shaped for aerodynamic properties. A solid state laser or: lasers are mechanically attached to the slider subsequent to its fabrication. An exemplary prior art attachment process involves careful positioning of the slider on an optical flat, applying a suitable quantity of adhesive or solder to the appropriate locations on the slider, and then urging the laser or lasers along the optical flat into position using micropositioners or microtranslation apparatus. This procedure is generally carried out under an optical microscope. When the adhesive cures, the emission face of the laser should be essentially flush with the slider air-bearing surface.
In the case of magneto-optic heads, additional magnetic components must generally be attached to the slider. Magneto-optic heads typically use a laser that is external to the slider, with laser output directed to the slider via optical fiber or fibers. A reflector and objective optics are coupled to the optical head to direct the laser output towards the magneto-optical medium. A flux element or coil is attached to the slider for magnetic recording or magnetically assisted recording, and magnetoresistive or giant magnetoresistive read element may be attached as well, together with conductors for the coil and magnetic read element.
The procedures for mechanical attachment of components to a slider are difficult and time-intensive. The machining and mechanical alignment tolerances for such attachment are high, generally on the order of 15 nanometers. Improper attachment of the laser and other components cannot generally be corrected. The preparation of optical and magneto-optic heads in this manner has thus involved considerable expense.
There is accordingly a need for a magneto-optical head apparatus and method which avoids complex, difficult and expensive mechanical attachment procedures for securing optical and magnetic components to a slider. The present invention satisfies this need, as well as others, and generally overcomes the deficiencies found in the background art.
The invention is a hybrid magnetic-optical head apparatus wherein one or more solid state lasers, magnetic field biasing elements, magnetic sensing elements, and an aerodynamically shaped slider comprise a single integrated, monolithic device fabricated from the same base semiconductor material into an optical head. The monolithic optical head can be quickly and easily attached to the read arm of an optical read/write device without requiring attachment of separate laser and magnetic elements, and without micropositioning or use of optical microscopy for positioning the lasers or magnetic elements.
More specifically, the invention is a hybrid magnetic-optical head apparatus comprising a single semiconductor substrate including a first, slider region having an air bearing surface, and a second, magnetic-optical function region having a semiconductor laser and at least one magnetic element. Preferably, the magnetic-optical function region of the substrate includes a magnetic field biasing element associated with the semiconductor laser, as well as a magnetic sensing element. The slider region preferably includes an aerodynamically shaped air cavity as well as the air bearing surface, and the emission face of the laser preferably is substantially co-planar with the air bearing surface.
The magnetic-optical function region may be configured for magnetically assisted thermal recording wherein writing is carried out primarily by laser power modulation to selectively heat portions of a medium, together with assistance of an applied magnetic field to establish a preferred direction of magnetization pattern in the medium. The magnetic-optical function region may alternatively be configured for thermally assisted magnetic writing wherein writing is carried out primarily by modulation of magnetic field, together with assistance of a laser which heats the medium to reduce the medium coercivity and thereby assist in the magnetic recording.
By way of example, and not necessarily of limitation, the semiconductor substrate preferably comprises a first conductivity-type clad layer or reflective layer, a second conductivity-type clad layer or reflective layer, an active region positioned between the first conductivity-type clad layer and second conductivity-type clad layer, and a base or substrate layer of first conductivity-type semiconductor material.
By way of further example, the first conductivity-type base layer preferably comprises a layer of n-semiconductor material, while the first conductivity-type clad layer is an n-clad layer, and the second conductivity-type-clad layer is a p-clad layer. The n-clad layer or reflective layer is adjacent a first side of the active region, and the p-clad layer or reflective layer is adjacent a second side of the active layer. Preferably, one or more insulating layers are included above or on top of the p-clad layer. The semiconductor substrate is formed or grown by conventional techniques such that the n-clad layer is deposited on the n-semiconductor base layer, the active region is deposited on the n-clad layer, and the p-clad layer is deposited on the active region. The outer surface of the n-semiconductor base layer defines the n-side of the substrate, while the outer surface of insulating layer proximate to the p-clad layer defines the p-side of the substrate.
A first section or portion of the semiconductor substrate provides a slider region and includes an air bearing surface and air cavity which are aerodynamically structured and configured to define a slider for the optical head. Preferably, the air bearing surface is formed on the outermost insulating layer on the p-side of the substrate. In other embodiments of the invention, an outermost metal layer may be included on the p-side of the substrate on top of the insulating layer, with the air bearing surface defined in the metal layer.
A second portion or section of the semiconductor substrate comprises a magnetic-optical function region which preferably includes a semiconductor laser and one or more magnetic elements. A p-electrical contact adjacent to the p-clad layer and an n-electrical contact adjacent to the n-semiconductor material layer on the opposite side of the semiconductor substrate define generally a diode laser structure across the substrate. The optical mode of the laser may additionally, or alternatively be defined by oxidized or ion-implanted regions associated with the p-clad layer or n-clad layer, as is well known in the art.
The magnetic elements in the magnetic-optical function region will generally include a magnetic field biasing element or flux element associated with the laser. In preferred embodiments of the invention utilizing a magnetically assisted thermal writing scheme, the magnetic field biasing element is preferably in the form of a magnetic coil surrounding the laser emission facet and positioned within or between insulating layers of the substrate surrounding the emission facet such that the magnetic coil is recessed with respect to the emission facet and air bearing surface.
In embodiments of the invention utilizing a thermally assisted magnetic writing scheme, the magnetic field biasing element preferably comprises a soft magnetic yoke element associated with the emission facet of the laser, together with one or more magnetic coils in association with the yoke. The magnetic-optical function region will also generally include a magnetic sensing or read element, preferably in the form of a giant magnetoresistive (GMR) sensor, which is preferably positioned such that its exposed edge is substantially co-planar with the laser emission facet and air bearing surface.
In one preferred embodiment of the invention, the active layer in the semiconductor substrate comprises a plurality of quantum well and quantum barrier structures. The p-clad layer preferably comprises a p-doped set of distributed Bragg reflector or DBR mirrors adjacent a first, upper surface of the active layer, and the n-clad layer preferably comprises an n-doped set of DBR mirrors adjacent a second, lower surface of the active layer. The p-doped DBR mirror set preferably comprises a plurality of p-doped, quarter wave dielectric layer pairs, and the n-doped DBR mirror set preferably comprises a plurality of n-doped quarter wave dielectric layer pairs. A p-doped semiconductor layer may be included between the quantum well active layer and the p-doped DBR mirror set, and an n-doped semiconductor layer may be included between the quantum well active region and the n-doped DBR mirror set. An insulating layer is positioned on a top or outer surface of the p-doped DBR mirror set, and a reflective metal layer is located on a top or outer: surface of the insulating layer. The n-doped semiconductor base layer is included adjacent a lower, outer surface of the n-DBR mirror set.
In another preferred embodiment of the invention, the p-electrical contact is provided as an annular-shaped metal pad in electrical contact with the top surface of the p-DBR mirror set. The n-side electrical contact is provided as a metal pad positioned in electrical contact with the n-type base semiconductor layer. The p-side and n-side contacts define a vertical cavity surface emitting laser (VCSEL) structure, with an emission facet provided in the center of the p-side contact. Preferably, an aperture is cut or etched through the outermost insulating layer or layers at the emission facet to provide for optical output from the emission facet in a narrow beam for near-field use.
The laser, magnetic field biasing element, and magnetic sensing element are all integral portions of the bulk semiconductor substrate which provides the slider region and magnetic-optical function region of the hybrid magnetic-optical head. In order to maintain the aerodynamic structure of the slider portion of the magnetic-optical head, the electrical conductors and connections associated with the laser, magnetic field biasing element, and magnetic sensing element on the p-side of the substrate must be structured and configured such that they do not extend above or otherwise interfere with the air bearing surface and air cavity of the slider portion. In this regard, the invention advantageously uses a plurality of conductive vias or through-ways which extend through the substrate, from the n-side to the p-side, so that all of the wire bonding pads necessary for the laser, magnetic field biasing element and magnetic sensing element can be located on the n-side of the substrate, well away or remote from the air bearing surface and air cavity on the p-side of the substrate.
Preferably, a first conductive via extends through the substrate and electrically connects a first wire bonding pad on the n-side of the substrate with a first conductor element on the p-side of the substrate. The first p-side conductor element in turn connects to the p-side electrical contact for the laser, so that electrical connection to the p-side laser contact can be achieved through the first n-side wire bonding pad. A second conductive via similarly extends through the substrate and electrically connects a second n-side wire bonding pad to a second p-side conductor element. The second p-side conductor element is connected to a plus (positive) contact for the magnetic field biasing element. Likewise, a third conductive via extends through the substrate and electrically connects a third n-side wire bonding pad to a third p-side conductor, which is in turn connected to a minus (negative) contact for the magnetic field biasing element. A fourth conductive via extends through the substrate and electrically connects a fourth n-side wire bonding pad to a fourth p-side conductor element, which in turn connects to a plus (positive) contact for the magnetic sensing element. In the same manner, a fifth conductive via extends through the substrate and electrically connects a fifth n-side wire bonding pad to a fifth p-side conductor element, which in turn connects to a minus (negative) for the magnetic sensing element.
The five p-side conductor elements are preferably recessed or flush with respect to the emission face of the magnetic-optical function region and air bearing surface of the slider region, so that the p-side electrical conductors do not extend above the air bearing surface, thereby maintaining the aerodynamic structure of the slider region. The outermost insulating layer or layers on the p-side of the substrate may cover one or more of the p-side electrical conductors, or, alternatively, one or more of the p-side electrical conductors may be recessed into the outermost insulating layer or layers.
The invention also provides a method for preparing an optical head which comprises, in general terms, preparing a semiconductor substrate, forming or defining at least one magnetic-optical function region on the semiconductor substrate, and forming or defining a slider region on the semiconductor substrate. More preferably, the preparing of the semiconductor substrate comprises providing a layer of n-semiconductor, depositing an n-clad layer thereon, depositing an active layer on the n-clad layer, depositing a p-clad layer on the active layer, and depositing at least one insulating layer on the p-clad layer. Forming the semiconductor substrate may additionally comprise depositing a metal layer on the insulating layer. The semiconductor substrate is preferably formed via conventional low-cost, high volume semiconductor fabrication methods using metal organic vaporphase epitaxy (MOVPE), liquid phase epitaxy (LPE), molecular beam epitaxy (MBE), or other deposition techniques.
The defining of the magnetic-optical function region preferably comprises depositing a p-side electrical contact on the p-clad layer and an n-side electrical contact on the n-semiconductor layer to define a diode laser structure across the substrate, depositing a magnetic field biasing element on an insulating layer proximate the p-side of the substrate and the emission facet of the laser, and depositing a magnetic sensor element on an insulating layer proximate the p-side of the substrate.
The defining of the magnetic-optical function region will also preferably comprise forming a plurality of conductive vias extending through the substrate, forming a plurality of n-side wire-bonding pads which connect to corresponding ones of the conductive vias, and forming a plurality of p-side conductor elements which connect to corresponding ones of the conductive vias, and which are also in electrical connection with the p-side electrical contact for the laser, p-side electrical contacts for the magnetic field biasing element, and p-side electrical contacts for the magnetic sensor element. The defining of the magnetic-optical is function region also preferably comprises etching or cutting an aperture through the outermost layer or layers on the laser emission facet.
The defining of the slider region is carried out by selecitvely depositing or etching an outermost insulating layer on the p-surface of the semiconductor substrate to define an air flow cavity, with the air-bearing surface being defined by the outer surface of the insulating layer around the air flow cavity. The air bearing surface is configured such that it is substantially co-planar with the emission face of the diode laser defined in the magnetic-optical function region. The material of the air bearing surface on the slider region, and the outermost layer on the emission facet may comprise the same material layer. In embodiments wherein an outer metal layer is included on the dielectric layer and an aperture is cut in the laser emission facet, the air bearing surface layer and outer layer of the emission facet will comprise the outer metal layer. Where the metal layer is omitted, the air bearing surface and emission facet will comprise the outermost dielectric layer of the substrate.
The semiconductor substrate may alternatively comprise an n-p, rather than a p-n structure, in which case the preparing of the semiconductor substrate would comprise providing a layer of p-semiconductor, depositing an p-clad layer thereon, depositing an active layer on the p-clad layer, depositing a n-clad layer on the active layer, and depositing at least one insulating layer on the n-clad layer.
The hybrid magnetic-optical head of the invention as thus prepared, is a single monolithic device made of a single substrate comprising an aerodynamic slider together with a semiconductor laser and one or more magnetic elements which are integral portions of the substrate. The invention thus avoids any complex and time-consuming positioning and attachment of the laser, magnetic elements, fiberoptics, or conductor elements on the slider, as has been heretofore required with previously used optical and magneto-optic heads.
The hybrid magnetic-optical head of the invention is preferably utilized in a near-field magnetic-optic system wherein the monolithic magnetic-optical head is mounted on a read/write arm via a suspension mechanism, and is used to read and write on magneto-optic media. The magnetic-optic system in accordance with the invention comprises generally a monolithic hybrid magnetic-optical head having a slider, an integral laser, an integral magnetic field bias element and a magnetic sensing element, a read/write arm coupled to the monolithic magnetic-optical head via a suspension mechanism, and an magneto-optic medium positioned adjacent to the monolithic magnetic-optical head. The laser in the magnetic-optical head preferably includes an aperture in an emission facet which is structured and configured for near-field use, wherein the width w of the aperture is generally of smaller dimension than the output wavelength xcex of the laser. The reflective read/write surface of the magneto-optical medium, during read/write operations, is preferably positioned at an optical path-length 1 from the laser emission facet such that the optical path-length 1 is generally less than or smaller than the output wavelength xcex.
The magneto-optic media used with the system of the invention preferably comprise thermomagnetic media having a readout layer and a memory or recording layer. The outer, readout layer may comprise, for example, a TbDyFeCo alloy or the like, while the inner, memory layer may comprise a TbFeCo alloy or the like. An outer protective coating of silicon nitride or a like material is preferably included proximate to the readout layer, and an inner protective coating of silicon nitride or a like material is preferably included proximate to the memory layer. The readout layer, memory layer and protective layers are preferably mounted on a substrate of polycarbonate, glass, or like substrate material.
The invention further comprises a near-field magnetic-optical method comprising providing an monolithic hybrid magnetic-optic head having an integral slider, laser, magnetic field biasing element and magnetic sensing element, positioning the monolithic magnetic-optic head adjacent to the a magneto-optic medium, and irradiating the optical medium with the laser while a magnetic field is simultaneously applied to the medium by the biasing element to effect writing on the medium. The writing may be carried out primarily via magnetically assisted thermal writing wherein laser power modulation provides thermal writing together magnetic field assistance from the magnetic field biasing element to effect magnetization in the medium, with or primarily via thermally assisted magnetic writing wherein writing is effected via modulation of magnetic field by the magnetic field biasing element together with thermal assistance from the laser to reduce coercivity in the medium.
The method of the invention also preferably comprises reading of the optical medium via a magnetic sensing element included on the magneto-optic head. A lubricant layer may be positioned between the magnetic-optic head and magneto-optic medium during reading and writing operations. Preferably, the laser includes an aperture in its emission facet of width w which is generally of smaller dimension than the output wavelength xcex of the laser, and the irradiating is carried out with the laser positioned such that the emission facet is positioned at an optical path-length 1 from the read/write surface of the medium, with the optical path-length being generally smaller than the output wavelength xcex.
Further advantages of the invention will be brought out in the following portions of the specification, wherein the detailed description is for the purpose of fully disclosing the preferred embodiment of the invention without placing limitations thereon.